Historically, ground roasted coffee beans have been brewed with hot water by any one variety of at least four different methods. Depending upon how the water is combined with the ground coffee, these methods and common names associated with the methods include (i) boiling and decoction, e.g. cowboy coffee, (ii) steeping or infusion, e.g., French press coffee, (iii) gravitational filtration, e.g., drip and percolator coffees, and (iv) pressurized filtration, e.g., espresso coffee. Each of these methods includes variations and, for producing an acceptable to good tasting coffee beverage, requires coffee beans ground to different average particle sizes. For example, boiled cowboy coffee utilizes coarse grounds (approximately 1 mm or greater diameter) where the grounds settle rapidly to the bottom of the pot. Boiled Turkish or mud coffee in the Middle East utilizes a finely ground coffee (less than 0.4 mm diameter) that is brought to a rapid boil with or without sugar one or more times and allowed to settle slowly to the bottom of the pot. Steeped French press coffee also utilizes a coarse ground coffee (1-1.5 mm diameter) in which a tall cylinder fitted with a metal and/or nylon mesh filter-plunger is used to move suspended coffee grounds to the bottom of the cylinder, enabling the filtered coffee to be poured out for drinking. Gravity filtration brewing methods include the drip process in which the coffee particles rest in an open filter with a filter support holder, and are typically bathed with hot water that is manually or automatically dispensed onto the coffee grounds for a few minutes before the coffee is poured. The filtration and percolator methods utilize a regular grind (approximately 1 mm diameter) or drip grind (approximately 0.75 mm diameter). With percolator brewing, boiling water is forced upward into a brewing chamber where, like drip brewing, simple gravity moves the water downward through the grounds. Unlike the drip method, percolator brewing passes the water upward and then downward over the grounds repeatedly. By contrast, classical pressurized filtration methods exemplified by the espresso and “moka pot” methods rely on highly pressurized hot water that is forced upward or downward a single time, through finely ground coffee grounds (approximately 200 microns or 0.2 mm diameter). While a moka pot may generate only about 1 bar (14-15 psi) of pressure, an espresso machine generally operates at ten times that pressure, forcing heated water at approximately 200° F. through a packed bed or “puck” of coffee grounds to produce between 1 and 2 ounces of highly concentrated coffee.
General information on matching approximate coffee particle size to the coffee brewing method being used is available. A certain amount of information can found on the web at for example: http://www.coffeegeek.com/pdfs/Baratza%20Grinders%20%20SM.pdf and http://www.coffeechemistry.com/grinding/grinding-fundamentals.html. The latter reference cites T. Lingle, “The Coffee Brewing Handbook”, Specialty Coffee Association of America (1996) for information on coffee particle size. These references are all in agreement, indicating that the typical coffee particle size for French press grind ranges up to approximately 1.3 mm, while coffee “regular grind” should average approximately 1.0 mm, drip grind approximately 0.7-0.8 mm, fine grind approximately 0.3-0.4 mm, and espresso grind 0.2-0.25 mm (200-250 microns).
Over the past twenty years, inventors at the Keurig Corporation have been awarded approximately 30 patents relating to (i) disposable beverage filter cartridges configured and adapted to store and subsequently brew ground coffee or tea particles, and (ii) automatic brewing machines designed to accommodate these filter cartridges and deliver individual servings of freshly brewed hot beverages. The filter cartridges are generally sized to provide single servings, and the machines are designed to deliver predetermined amounts of low pressure heated water, e.g., between 4 and 12 ounces of water at a temperature of approximately 192° F. Duffy et al. in U.S. Pat. No. 6,672,200 describes in considerable detail the controlled operation of a typical automated Keurig-type beverage brewing system. One of the control systems employs sensors that control and limit air pressure delivering heated water through a brewing cartridge (holding coffee grounds or tea leaves, for example) to a range of between approximately 1.5 and 7 psi (between 0.1 atm and 0.5 atm or bar of pressure). Sylvan et al. describes an improved beverage filter cartridge in U.S. Pat. No. 5,325,765 for use in an automatic brewing machine. Such brewing machines that are adapted to hold disposable filter cartridges are described in a number of other patents assigned to Keurig, Inc., such as U.S. Pat. No. 6,142,063 by Beaulieu et al. The filter cartridge of Sylvan et al. is small and compact, yet allows a high water flow rate. Aiding in achieving their objectives, a highly permeable coffee filter is provided. The filter can be formed from a synthetic non-woven and water-permeable material such as polypropylene or polycarbonate fibers, selected to be strong and self-supporting when wet. The cartridge is generally hermetically sealed above and optionally below the dry coffee or tea held in the filter so as to preserve product freshness. At the time of use, the upper cartridge sealing membrane (and lower sealing membrane, if present) are typically punctured by a sharp and rigid hollow tube device as the lid of the brewing machine is closed. The hollow tube delivers low-pressure hot water that subsequently enters and exits the cartridge. A gasket positioned around the water injection tube contacts the cartridge's upper sealing membrane to establish a pressure seal. This seal allows adequate water pressure, e.g., between 0.1 and 0.5 bar, to be maintained over and through the bed of coffee grounds and support filter to push the coffee beverage out of the cartridge.
Many patents have been directed to the design of single use coffee filter cartridges and accompanying automatic brewing machines. However, the literature is lacking a description of the engineering and tailoring of coffee grounds for use in single serving coffee filter cartridges. There is little information available on suitable coffee particle size for use in single serving filter cartridges that are brewed in coffee machines such as Keurig's B70 Platinum single cup brewing system (Keurig Corporation, Reading, Mass.). This method of brewing coffee required development of single serving filter cartridges containing ground coffee (U.S. Pat. No. 5,325,765 by Sylvan et al.) and an accompanying automatic brewing machine (U.S. Pat. No. 6,142,063 by Beaulieu et al.). To the extent that the filter cartridge brewing process has both similarities and differences from the drip and the espresso methods, it is difficult to predict what size of coffee particle is suitable for filter cartridge coffee brewing.
The present technology is directed to overcoming these and other deficiencies in the art.